Nucleation inhibition despite lower glass viscosities? - Effect of the B2O3, Na2O and K2O addition on the crystallization behavior of lithium disilicate glasses

Stoichiometric lithium disilicate glasses were doped with up to 2 mol% B2O3, Na2O or K2O and the crystallization kinetics were determined as a function of the temperature using in situ hot-stage microscopy. The additives lead to a decrease of the glass viscosities in the studied temperature range with the exception of the boron-containing samples which show slightly higher viscosities in the nucleation range. While in the boron-containing samples, lithium disilicate solid solutions precipitate during thermal treatment, in the other samples a mixture of lithium disilicate, lithium metasilicate and cristobalite was detected. The steady-state nucleation rates decrease by up to one order of magnitude and especially in the case of the additive B2O3, the induction times for nucleation are remarkably longer. While the additives B2O3 and K2O lead to a decrease of the crystal growth velocities, in case of Na2O, the contrary effect can be noticed. Possible reasons for the observed effects are discussed.